1033 51ST PL SW Geotech Report 2022-10-28

Trench backfill material should be compacted to not less than 95 percent of the maximum dry density, as determined byASTM D1'557. Pipe bedding should be compacted to 90 percent of the maximum dry density, as determined by ASTM D1557. Trench backfill should be placed in lifts that do not exceed 12 inches before compaction. 'City standard drawings should be consulted for additional compaction requirements. 8.4 TEMPORARY SLOPES Temporary slopes less than 10 feet high should be no steeper than 1 H:1 V, provided groundwater seepage does not occur. If slopes greater than 10 feet high are required, GeoDesign should be Contacted to make additional recommendations. We recommend a minimum horizontal distance of 5 feet from the edge of the existing improvements to the top of the temporary slope. All cut slopes should be protected from erosion by covering them during wet weather. If sloughing or instability is observed, the slope should be flattened or supported by shoring. Excavations should not undermine adjacent utilities, foundations, walkways, streets, or other hardscapes unless special shoring or underpinned support is provided. 8.5 EROSION CONTROL The on-site soil is moderately susceptible to erosion. Consequently,we recommend that slopes be covered with an appropriate erosion control product if construction occurs during periods of wet weather. We recommend that all slope surfaces be planted as soon as practical to minimize erosion.' Surface water runoff should be collected and directed away from slopes to prevent water from running down the slope face. Erosion control measures such as straw bales, sediment fences, and temporary detention and settling basins should be used in accordance with local and state ordinances. 8.6 LID'INFILTRATION ELEMENTS We understand that pervious LID infiltration elements such as permeable pavement, bioretention, and/or infiltration trenches may be incorporated into the project to address stormwater management.. Recommendations for their design and construction are provided below. 8.6.1 Subgrade Preparation The exposed subgrade at the base of the planned LID infiltration elements should be scarified to a depth of 12 inches and compacted to a firm condition (between 90 and 92 percent of the maximum dry.density,as-determined by ASTM D1557) prior to placement of storage aggregate. Over-compaction of the subgrade and exposure to construction'traffic should be avoided. The subgrade for permeable pavement can be sloped up to 2 percent but should be relatively flat, if possible, to prevent uneven ponding of water within the storage aggregate. If unsuitable, soft, or saturated materials are identified during subgrade preparation, the material should be removed to expose firm material or to a maximum depth of 2 feet. The excavated material should'be replaced with storage aggregate. 8.6.2 `. Subgrade Separation Geotextile The soil present at the anticipated base of the proposed infiltration elements consists of a gray brown, silty sand with gravel with a fines content greater than 7 percent passing the U.S. Standard No. 200 sieve. ,The City requires the placement of a non-woven geotextile between GEODESIGNY ,,